Liquid- or liquid crystal-sealing materials (sealants) are used in LCDs, dye-sensitized solar cells, organic El devices, and so on. For example, such materials are used as a sealant for liquid crystal materials in LCDs, as a sealant for an organic solvent electrolyte (e.g., acetonitrile or propylene carbonate) or an ionic liquid in dye-sensitized solar cells, and as a material for forming a dam which is to be filled with a liquid sealant in solid encapsulation in organic EL devices. Because conventional sealants are brought into contact with a liquid or liquid crystals in their uncured state, there is a problem that a resin component or the like leaches from the sealant to contaminate a device, resulting in impairment in device performance and reliability. Additionally, the sealant becomes brittle as a result of leaching and can break easily. Thus, a non-leaching sealant that does not contaminate a liquid or liquid crystals has been sought for.
The ODF technique for LCD production has been replacing conventional vacuum-capillary filling for the purpose of processing time saving. The ODF method includes the steps of applying a sealant to a first electroded substrate to a pattern of a display frame using a dispenser, dropping liquid crystals inside the frame, attaching a second electroded substrate to the first substrate in vacuo, temporarily curing the sealant by UV irradiation, and heating the liquid crystals and the sealant to anneal the liquid crystals and to complete curing of the sealant. According to the ODF method, curing the sealant in two stages, i.e., photocure and thermal cure, allows reduction of curing time, which leads to shortening the processing time for the LCD manufacturing.
In order for an LCD panel to display as much information as possible on one screen, LCD panels have shown tendencies to higher resolution and faster response time.
In recent years, mother glass has been designed to yield the maximum number of LCD panels. With these tendencies, LCD panel manufacturers have come to apply a liquid crystal-sealing material (sealant) onto the black matrix of the substrate having color filters or over the TFT wires on the counter substrate (TFT substrate). Whichever side a UV radiation is applied to, the black matrix or the TFT wire will shadow the sealant from the UV radiation. The sealant in shadow can remain uncured to allow its component to leach into liquid crystals on thermal curing, resulting in reduction of display qualities in the vicinities of the seal.
It has therefore been demanded to develop a photo radical initiator and a sealant containing the same that is able to photocure even deep in its portion shadowed from light and involves little leaching into liquid crystals.
Liquid crystal compounds having an alkenyl group having a small rotational viscosity coefficient are used in most nematic liquid crystal materials for TFT-LCDs of TN, VA, IPS, or other modes for the purpose of raising response speed to address moving images. As stated, when an uncured sealant contacts a liquid crystal material, a photo radical initiator is leached from the sealant into the liquid crystal material to induce photo deterioration of the alkenyl group.
Patent literature 1 through 7 (see below) disclose liquid crystal sealants containing a photo radical initiator having an oxime ester structure. The conventional photo radical initiators having an oxime ester structure which have insufficient sensitivity provide a weakly cured product from which the resinous component or the initiator itself can leach into a liquid crystal material, resulting in reduction of electrical characteristics. Even those having high sensitivity involve the problem that their decomposition product can dissolve into a liquid crystal material to damage the electrical characteristics.